1. Field of the Invention
The present invention relates to a polypropylene-based resin composition, which is superior in rigidity and impact resistance in respect of physical properties, and has a short molding cycle in respect of injection moldability and is characterized in that its molded article is excellent in surface quality, for example, the molded article has neither flow mark nor weld line and is free from surface strain. More particularly, it relates to a polypropylene-based resin composition comprising a major amount of a specific polypropylene-based resin, a minor amount of a specific ethylene-octene copolymer rubber and talc, which is superior in physical properties and injection moldability as described above, and an injection-molded article having excellent dimensional stability obtained by subjecting the same to injection-molding, particularly injection-molded article for automobile interior parts (e.g. instrument panel, door-trim, pillar).
2. Prior Art
Crystalline propylene-ethylene block copolymers have recently been used as automobile interior materials in view of lightening and cost saving. However, conventional crystalline propylene-ethylene block copolymer materials had a low impact strength and contained a large amount of an inorganic filler for improving rigidity, thermal properties such as heat distortion temperature and the like. Therefore, the specific gravity was relatively high.
In JP-A-53-22552, 53-22552, 6-192500, 6-248156, 6-192506 or 53-40045, it is disclosed to incorporate an ethylene-propylene copolymer rubber and an ethylene-octene copolymer rubber into a crystalline propylene-ethylene block copolymer to improve the impact strength. However, the rigidity and thermal properties such as heat distortion temperature, etc. for the automobile interior material become inferior because the ethylene-propylene copolymer rubber and ethylene-octene copolymer rubber are incorporated. In JP-A-51-136735, 53-64256, 53-64257, 57-55952, 57-207630, 58-17139, 58-111846 or 59-98157, or JP-B-55-3374, it is disclosed to incorporate an inorganic filler such as calcium carbonate, barium sulfate, mica, crystalline calcium silicate, talc, or the like to improve the rigidity and thermal properties.
In such way, a composition of crystalline propylene-ethylene block copolymer/ethylene-propylene copolymer rubber or ethylene-octene copolymer rubber (abbreviated to "ethylene-propylene or ethylene-octene copolymer rubber composition" hereinafter) has widely been used as the automobile interior material due to its low cost and good moldability. However, it is required to develop a material improved in better balance between impact strength and rigidity by improving the ethylene-propylene copolymer rubber component.